Digital Automatic Flight Control is the Answer - What is the Question?

Beginning with process controls in the mid fifties, digital control systems have seldom met all the claimed advantages and in many cases have been outright failures. Airborne digital computers have just begun to appear in the commercial jet transport market after several years of experimental and military development. The success of these systems in meeting user expectations has not been overwhelming, which leads to the question: Why change from known analog flight control technology to digital? This paper examines that question by reviewing the state of the art in analog flight control system technology and evaluating this against current airline problems. A realistic means of evaluating claimed advantages for new technology is thus established. The advertised solutions of digital technology to analog problems are examined and, in some cases, debunked. However, consideration of the real problems and the capabilities of digital systems leads to the conclusion that there is a real payoff. Evidence from background studies at Boeing is offered to support this conclusion. A description of the digital flight control system electronics (FCSE) development program for the new Boeing 7×7 airplane is also provided. This program is currently in progress, and its specific objective is to assure that the real payoff is achieved for the subsequent production system.